A drought is an extended period where water availability falls below the statistical requirements for a region. Drought is not a purely physical phenomenon, but instead is an interplay between natural water availability and human demands for water supply.
The precise definition of drought is made complex due to political considerations, but there are generally three types of conditions that are referred to as drought.
Meteorological drought is brought about when there is a prolonged period with below average precipitation.
Agricultural drought is brought about when there is insufficient moisture for average crop or range production. This condition can arise, even in times of average precipitation, due to soil conditions or agricultural techniques.
Hydrologic drought is brought about when the water reserves available in sources such as aquifers, lakes, and reservoirs falls below the statistical average. This condition can arise, even in times of average (or above average) precipitation, when increased usage of water diminishes the reserves.
When the word "drought" is used commonly, the most often intended definition is meteorological drought. However, when the word is used by urban planners, it is more frequently in the sense of hydrologic drought.
Periods of drought can have significant economic and social consequences. The most famous example of this was seen in the dustbowl of the 1920s and 1930s, when entire districts of the American Great Plains were depopulated by a combination of drought and economic recession.
Drought can often be the precipitating factor that causes famine, in particular in countries without extensive economic resources.
The drought indicators that are synthesized into the Drought Monitor map are on this website, under Forecasts and Current Conditions.
In contrast, drought classifications persisted or worsened farther to the south and east, with D0 conditions encompassing the Twin Cities area, and conditions on the Keweenaw Peninsula in northwestern Michigan deteriorated to D2.
In Alabama, 68 percent of the cotton crop, 48 percent of peanuts, and 78 percent of pastures are in poor or very poor condition, as are 60 percent of Florida peanuts and 35 percent of Georgia cotton.
Physiologicaldrought is a condition afflicting plants that have been exposed to too much salt, preventing them from absorbing water from soil.
Decision makers at all levels need to decide ahead of time on an operational definition of drought that is relevant for their circumstances, and what actions they will take when they are in a drought.
These droughts spurred the migration of much of the population to locations such as New England, to participate in the whaling industry.
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